The present invention relates to a simulated neon illumination device using a waveguide, and, more particularly, to a simulated neon illumination device in which high-intensity diodes are used to illuminate the respective ends of the waveguide.
Neon lighting, which is produced by the electrical stimulation of the electrons in the low-pressure neon gas-filled glass tube, has been a main stay in advertising and for outlining channel letters and building structures for many years. A characteristic of neon lighting is that the tubing encompassing the gas has an even glow over its entire length irrespective of the viewing angle. This characteristic makes neon lighting adaptable for many advertising applications, including script writing and designs, because the glass tubing can be fabricated into curved and twisted configurations simulating script writing and intricate designs. The even glow of neon lighting being typically devoid of hot spots allows for advertising without visual and unsightly distractions. Thus, any illumination device that is developed to duplicate the effects of neon lighting must also have even light distribution over its length and about its circumference. Equally important, such lighting devices must have a brightness that is at least comparable to neon lighting. Further, since neon lighting is a well established industry, a competitive lighting device must be lightweight and have superior “handleability” characteristics in order to make inroads into the neon lighting market. Neon lighting is recognized as being fragile in nature. Because of the fragility and heavy weight, primarily due to its supporting infrastructure, neon lighting is expensive to package and ship. Moreover, it is extremely awkward to initially handle, install, and/or replace. Any lighting device that can provide those previously enumerated positive characteristics of neon lighting, while minimizing its size, weight, and handleability shortcomings, will provide for a significant advance in the lighting technology.
Aforementioned U.S. application Ser. No. 09/982,705, now U.S. Pat. No. 6,592,238, describes in detail an illumination device that utilizes high-intensity point light soirees in combination with a rod of material having “leaky” optical waveguide characteristics. For purposes of this description, a “leaky waveguide” is defined as a waveguide in which the structure and/or material is designed such that light traveling along the longitudinal length of the waveguide is caused to be diverted so as to be emitted out of the lateral surface of the waveguide. This redirection of the light can be accomplished through light scattering by the waveguide material itself or through structural designs of the waveguide. In U.S. application Ser. No. 09/982,705, now U.S. Pat. No. 6,592,238, the point light sources are aligned near one lateral surface of the waveguide rod such that emitted light is directed into the lateral surface, is preferentially scattered along the length of the waveguide rod, and exits in a very uniform pattern out of the lateral surface of the waveguide rod facing the observer of the light. The intensity and the uniformity of the exiting light approaches that of neon tubing. Moreover, the tubing is light, very resistant to breakage, and has very light supporting infrastructure. The operating temperature of the illumination device is also significantly less than typical neon lighting and may be used in aqueous environments.
The simulated neon lighting as described above and in the aforementioned co-pending application does require that the point light sources be aligned along substantially the entire length of the optical waveguide rod to provide for the proper and acceptable simulation of neon lighting. For long lengths of waveguide, large numbers of point light sources are required with commensurate lengths of light-directing structure for efficiently directing emitted light into the light receiving surface of the waveguide rod. The additional numbers of point light sources and light-directing structure increases manufacturing and material costs, particularly for long lengths of waveguide rods. Thus, it would be desirable to have an illumination device in which the additional costs could be substantially reduced.
An illumination device using the aforementioned leaky waveguide that is illuminated at the ends of the waveguide rod is described in U.S. application Ser. No. 09/844,212, now U.S. Pat. No. 6,550,652. This application sets forth various techniques to direct the light out of the lateral surface of the waveguide, including the use of reflective strips or painted stripes along a portion of the lateral surface to help direct light incident on the strip or painted stripes out of the lateral surface largely opposite to the portion supporting the reflective strips or painted stripes. Other techniques for causing the waveguide to leak light laterally are also described including notching the lateral region or providing holographic layers of material. Still another disclosed technique is the use of material such as DR acrylic material to cause the described scattering of the light out of the lateral surface of the waveguide rod. The end-lit illumination device thus has many applications, particularly when used to illuminate script or designs on the light-emitting lateral surface of the waveguide. However, the use of end-lit configurations in an attempt to simulate neon lighting, particularly when longer lengths are needed, have resulted in a significant problem due to the pronounced attenuation of the light toward the center of the illumination device. Part of this noticeable attenuation can be attributed to the relative weak luminosity of the present generation of LEDs, typically up to approximately 120 lumens. As the length of the leaky waveguide rod is increased, the attenuation becomes much more noticeable. FIG. 1A illustrates graphically the normalized brightness as a function of the distance from the LEDs in a typical leaky end-lit waveguide as described in the aforementioned patent application Ser. No. 09/844,212, now U.S. Pat. No. 6,550,652. As shown, the brightness or intensity of the light decreases significantly after a short distance. This attenuation of the light intensity is due in part to the absorption of the light by the material comprising the waveguide rod and the continuous loss of light due to the designed leaking of light out of the treated waveguide rod. When a reflecting cap is placed over the end opposite the light source to reflect back, the light successfully traveling the length of the waveguide rod, an observer will see light being emitted by the lateral surface of the rod with the intensity of the light falling progressively off from the end closest to the light source and then rising slightly toward the reflecting end, as illustrated graphically in FIG. 1B. The slight increase is believed to be due to the leaking of the reflected light along the length of the waveguide immediately adjacent to the reflecting cap.
To some extent, the intensity and attenuation problems can be partially addressed by using two LEDs groups, respectively housed adjacent and illuminating each end of the waveguide rod. Using two LED groups is particularly beneficial with extended lengths of the leaky waveguide rod. Since the total light flux entering the waveguide rod is increased two-fold, the intensity of the light being emitted along the lateral surface is noticeably brighter. Aforementioned U.S. Pat. application Ser. No. 09/844,212, now U.S. Pat. No. 6,550,652 illustrates a leaky waveguide rod with two groups of LEDs. FIG. 1C is an attenuation graph representing a waveguide rod with a LED positioned at each end, illustrating the resultant intensity curve for such a configuration. Unfortunately, while the overall intensity is increased as compared to a waveguide rod lit at only one end, the resultant intensity curve clearly demonstrates that the undesirable attenuation is still present, particularly near the midpoint of the waveguide.
Thus, it is a paramount object of the present invention to provide for an illumination device with an end-lit waveguide rod that approaches neon/fluorescent lighting in both uniformity of the emitted light out of the lateral surface of the rod and overall intensity, while minimizing the need for numerous LEDs as point light sources.
Still another object of the present invention is to provide for an illumination device with an end-lit waveguide rod that efficiently directs the light emitted out of the associated LEDs into one or both end of the waveguide rod and that efficiently leaks the light out of the lateral surface of the waveguide rod in a preferred direction.
Yet another object of the present invention is to provide for an illumination device with an end-lit waveguide rod that effectively addresses the problems of intensity light attenuation occurring in extended waveguide rods.
Other objects and advantages of the present invention will become readily apparent upon a reading of the detailed description along with the appended drawings.